Imagesetters and platesetters are used to expose substrates that are used in many conventional offset printing systems. Imagesetters are typically used to expose the film that is then used to make the plates for the printing system. Platesetters are used to directly expose the plates.
For example, plates are typically large substrates that have been coated with photosensitive or thermally sensitive material layers, referred to the emulsion. For large run applications, the substrates are fabricated from aluminum, although organic substrates, such as polyester or paper, are also available for smaller runs.
Computer-to-plate printing systems are used to render digitally stored print content onto these printing plates. Typically, a computer system is used to drive an imaging engine of the platesetter. In a common implementation, the plate is fixed to the outside or inside of a drum and then scanned with a modulated laser source in a raster fashion. In other implementations, the plate is held on a flatbed.
The imaging engine selectively exposes the emulsion that is coated on the plates. After this exposure, the emulsion is developed so that, during the printing process, inks will selectively adhere to the plate""s surface to transfer the ink to the print medium.
Typically, one of two different strategies is used to feed substrates to the imaging engine in the printing system. In the simplest case, an operator manually places individual substrates into a feeder that then conveys the substrates through a feed port to the drum scanner. This approach, however, has some obvious drawbacks. First, an operator must be dedicated to feeding the substrates. And, the printing system must be housed within a lightsafe environment, if the substrates being used have any sensitivity to ambient light. The alternative approach is to use a substrate manager.
Managers typically house multiple substrate cassettes. Each cassette is capable of holding many substrates in a stack. The substrates are separated by slip sheets that are used to protect the plate emulsions from damage. For example, in one common implementation, each cassette holds up to one hundred substrates. The manager selects substrates from one of its cassettes and then feeds the substrates, automatically, into the imaging engine, while removing the slip sheets.
In these designs, cassettes are loaded into the manager on a table. The table is then raised and lowered inside the manager to bring the substrates of a selected cassette into cooperation with a picker that grabs individual substrates and feeds them to the imaging engine.
The present invention is directed to a substrate manager for a substrate exposure machine. One example of such a machine would be a platesetter. As such, it comprises a substrate storage system, containing one or more stacks of substrates, such as plates in one implementation. A substrate picker is provided for picking substrates from the stack of substrates. The substrates are then handed to a transfer system that conveys the substrates to an imaging engine.
According to the invention, a substrate inverter system is also provided. This system inverts the substrates from being emulsion side down to emulsion side up in the present implementation. This allows plates, for example, which are stored emulsion side down in storage devices such as cassettes, to be inverted to an emulsion side up orientation, and then transferred, using the substrate transfer system to the imaging engine. This prevents damage to the emulsion on the plates, which can be very sensitive to any surface contact.
This inverting process has some advantages. First, the plates can be picked from the non-emission side so that the picker""s suction cups will not mar the emulsion. Further, the plates are emulsion side up during the transfer. This further prevents any damage to the sensitive plate emulsions. Moreover, the plates, now in an emulsion side up configuration, are in the right orientation for being installed on the outside periphery of a drum on an external drum imaging system, as is common in many platesetters.
In specific embodiments, the substrate storage system is capable of containing multiple cassettes, each holding separate stacks of substrates. The substrate picker includes a substrate peeler for separating a substrate from the stack of substrates. A sheet separator is also provided to ensure that a sheet separating the substrates, typically used to protect the plate emulsions, is separated from the substrate that is being picked by the substrate picker.
In the preferred embodiment, the substrate inverter system comprises an arcuate transfer path over which substrates are carried to invert the substrates and transfer the substrates between the substrate storage system and the substrate transfer system.
In the current implementation, the substrate inverter system specifically comprises an advancing or leading arm and a trailing, or lagging, arm for carrying the substrates over the arcuate transfer path. The leading arm carries headers of the substrates and the lagging arm carries lagging edges.
In other embodiments a curved conveyor system is used, for example.
In general, according to another aspect, the invention features a plate inverter for a platesetter system. The plate inverter comprises a plate picker for picking a plate and an arcuate transfer path, over which the plate is conveyed between the plate picker and an imaging engine.
In general, according to still another aspect, the invention features a method of managing substrates in a substrate exposure machine. This method comprises storing substrates to be exposed in a stack of substrates and then picking the substrates from this stack. The substrates are subsequently inverted and then conveyed, after being inverted, to an imaging engine.
The above and other features of the invention including various novel details of construction and combinations of parts, and other advantages, will now be more particularly described with reference to the accompanying drawings and pointed out in the claims. It will be understood that the particular method and device embodying the invention are shown by way of illustration and not as a limitation of the invention. The principles and features of this invention may be employed in various and numerous embodiments without departing from the scope of the invention.